Method and apparatus for detecting atrial filling pressure

ABSTRACT

A cardiac rhythm management system provides for ambulatory monitoring of hemodynamic performance based on quantitative measurements of heart sound related parameters for diagnostic and therapeutic purposes. Monitoring of such heart sound related parameters allows the cardiac rhythm management system to determine a need for delivering a therapy and/or therapy parameter adjustments based on conditions of a heart. This monitoring also allows a physician to observe or assess the hemodynamic performance for diagnosing and making therapeutic decisions. Because the conditions of the heart may fluctuate and may deteriorate significantly between physician visits, the ambulatory monitoring, performed on a continuous or periodic basis, ensures a prompt response by the cardiac rhythm management system that may save a life, prevent hospitalization, or prevent further deterioration of the heart.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation-in-part of commonly assigned Siejkoet al. U.S. patent application Ser. No. 10/334,694, entitled “METHOD ANDAPPARATUS FOR MONITORING OF DIASTOLIC HEMODYNAMICS,” filed Dec. 30,2002, which is hereby incorporated by reference.

TECHNICAL FIELD

This document relates generally to cardiac rhythm management systems andparticularly, but not by way of limitation, to such a system sensingheart sounds for monitoring, diagnosis, and therapy control.

BACKGROUND

A heart is the center of a person's circulatory system. It includes acomplex electromechanical system performing two major pumping finctions.The left portions of the heart, including the left atrium and the leftventricle, draw oxygenated blood from the lungs and pump it to theorgans of the body to provide the organs with their metabolic needs foroxygen. The right portions of the heart, including the right atrium andthe right ventricle, draw deoxygenated blood from the organs and pump itinto the lungs where the blood gets oxygenated. These mechanical pumpingfunctions are accomplished by contractions of the myocardium (heartmuscles). In a normal heart, the sinus node, the heart's naturalpacemaker, generates electrical signals, called action potentials, thatpropagate through an electrical conduction system to various regions ofthe heart to excite myocardial tissues in these regions. Coordinateddelays in the propagations of the action potentials in a normalelectrical conduction system cause the various regions of the heart tocontract in synchrony such that the pumping functions are performedefficiently. Thus, the normal pumping functions of the heart, indicatedby hemodynamic performance, require a normal electrical system togenerate the action potentials and deliver them to designated portionsof the myocardium with proper timing, a normal myocardium capable ofcontracting with sufficient strength, and a normal electromechanicalassociation such that all regions of the heart are excitable by theaction potentials.

The function of the electrical system is indicated byelectrocardiography (ECG) with at least two electrodes placed in orabout the heart to sense the action potentials. When the heart beatsirregularly or otherwise abnormally, one or more ECG signals indicatethat contractions at various cardiac regions are chaotic andunsynchronized. Such conditions are known as cardiac arrhythmias.Cardiac arrhythmias result in a reduced pumping efficiency of the heart,and hence, diminished blood circulation. Examples of such arrhythmiasinclude bradyarrhythmias, that is, hearts that beat too slowly orirregularly, and tachyarrhythmias, that is, hearts that beat tooquickly. A patient may also suffer from weakened contraction strengthrelated to deterioration of the myocardium. This further reduces thepumping efficiency. For example, a heart failure patient suffers from anabnormal electrical conduction system with excessive conduction delaysand deteriorated heart muscles that result in asynchronous and weakheart contractions, and hence, reduced pumping efficiency, or poorhemodynarnic performance. Thus, in addition to ECG, the function of themechanical system and the electromechanical association need to bemeasured to assess the overall pumping performance of the heart.

Characteristics of heart sounds are known to be indicative of variousmechanical properties and activities of the heart. Measurementsperformed with synchronously recorded ECG and heart sounds provide forquantitative indications of the electromechanical association. Forexample, amplitudes of the third heart sound (S3) and fourth heart sound(S4) are related to filing pressures of the left ventricle duringdiastole. Fundamental frequencies of S3 and S4 are related toventricular stiffness and dimension. Chronic changes in S3 amplitude iscorrelated to left ventricular chamber stiffness and degree ofrestrictive filling. Change in the interval between atrial contractionand S4 is correlated to the changes in left ventricular end diastolicpressure. Such parameters, being correlated to the heart's mechanicalproperties and electromechanical association, quantitatively indicateabnormal cardiac conditions, including degrees of severity, and need ofappropriate therapies.

For these and other reasons, there is a need for a system providing forcardiac therapy based on parameters related to heart sounds.

OVERVIEW

A system provides for ambulatory monitoring of hemodynamic performancebased on quantitative measurements of heart sound related parameters fordiagnostic and therapeutic purposes. Monitoring of such heart soundrelated parameters allows the system to determine a need for deliveringa therapy and/or therapy parameter adjustments based on conditions of aheart. This monitoring also allows a physician to observe or assess thehemodynamic performance for diagnosing and making therapeutic decisions.The monitoring can also be used to trigger an alert to notify a patientor a caregiver. Because the conditions of the heart may fluctuate andmay deteriorate significantly between physician visits, the ambulatorymonitoring, performed on a continuous or periodic basis, ensures aprompt response by the system that may save a life, preventhospitalization, or prevent further deterioration of the heart.

In one embodiment, a system includes an acoustic senor, a cardiacsensing circuit, a heart sound detector, a parameter generator, aprocessor, and a therapy circuit. The acoustic sensor senses an acousticenergy and produces an acoustic sensor signal indicative heart sounds.The cardiac sensing circuit senses a cardiac signal indicative ofcardiac electrical events. The heart sound detector detects selectedheart sounds based on the acoustic sensor signal and the cardiac signal.The parameter generator generates values of at least one predeterminedparameter related to the selected heart sounds. The processor includes atrending analyzer that produces and analyzes at least one trend relatedto the selected heart sounds based on the values of the predeterminedparameter. The therapy circuit delivers cardiac therapy with at leastone therapy parameter determined based on the trend.

In another embodiment, an acoustic energy is sensed to produce anacoustic sensor signal indicative heart sounds. One or more cardiacsignals indicative of cardiac electrical events are also sensed.Selected heart sounds are detected. Parameter values related to theselected heart sounds and selected cardiac electrical events aregenerated. Selected parameter values, which are associated with one ormore types of the selected heart sounds, are analyzed to produce atleast one trend. A therapy, with at least one parameter determined basedon the trend, is delivered.

In yet another embodiment, a system includes an implantable device. Theimplantable device includes an acoustic sensor, a cardiac sensingcircuit, a gating module, a heart sound detector, a measurement module,and a therapy circuit. The acoustic sensor senses an acoustic energy toproduce an acoustic sensor signal indicative heart sounds. The cardiacsensing circuit senses at least one cardiac signal indicative of cardiacelectrical events. The gating module generates heart sound detectionwindows each timed for detection of one of selected heart sounds basedon a time of occurrence of one of selected cardiac electrical events.The heart sound detector detects the selected heart sounds. Themeasurement module generates parameter values related to the selectedheart sounds. The therapy circuit delivers a therapy based on theparameter values.

In Example 1, a system includes an implantable medical device. Theimplantable medical device includes a heart sound sensor, configured tosense a heart sound signal of a heart. The system also includes a heartsound detector, coupled to the heart sound sensor, the heart sounddetector configured to detect at least one parameter indicative of anatrial filling pressure of the heart using the heart sound signal. Thesystem also includes a processor, coupled to the heart sound detector,the processor configured to compare the at least one parameter to athreshold.

In Example 2, the atrial filling pressure of Example 1 optionallyincludes a left atrial filling pressure.

In Example 3, the at least one parameter of Examples 1-2 optionallyincludes at least one measurement, feature, characteristic, computation,or interval of the heart sound signal. In Example 4, the at least onemeasurement, feature, characteristic, computation, or interval of theheart sound signal of Examples 1-3 optionally includes at least one ofan amplitude of a third heart sound (S3), a split second heart sound(S2) time interval, an S2-S3 time interval, and a normalized amplitudeor interval of at least one measurement, feature, or characteristic ofthe heart sound signal.

In Example 5, the implantable medical device of Examples 1-4 optionallyincludes a cardiac sensor, coupled to the heart sound detector, thecardiac sensor configured to sense a cardiac signal of the heart. Theheart sound detector of Examples 1-4 is also optionally configured todetect the at least one parameter using the heart sound signal and thecardiac signal.

In Example 6, the at least one parameter of Examples 1-5 optionallyincludes at least one measurement, feature, characteristic, computation,or interval between at least one cardiac signal feature and at least oneheart sound signal feature.

In Example 7, the at least one parameter of Examples 1-6 optionallyincludes a systolic time interval (STI).

In Example 8, the threshold of Examples 1-7 optionally includes apredefined threshold.

In Example 9, the threshold of Examples 1-8 optionally includes anabsolute threshold.

In Example 10, the system of Examples 1-9 optionally includes a posturesensor, coupled to the processor, the posture sensor configured to sensea posture signal. The processor of Examples 1-9 is also optionallyconfigured to compare the at least one parameter to the threshold usingthe posture signal.

In Example 11, the system of Examples 1-10 optionally includes an alertmodule, coupled to the processor, the alert module configured togenerate an alert using the at least one parameter.

In Example 12, the alert of Examples 1-11 is optionally configured to begenerated with a predefined specificity.

In Example 13, the alert of Examples 1-12 is optionally configured to begenerated with a predefined specificity equal to or greater than 85%.

In Example 14, the alert of Examples 1-13 is optionally configured to begenerated with a predefined specificity equal to or greater than 90%.

In Example 15, a system includes means for sensing a heart sound signalof a heart using an implanted heart sound sensor, such as by using aheart sound sensor to sense the heart sound signal of the heart. Thesystem also includes means for detecting at least one parameterindicative of an atrial filling pressure of the heart using the heartsound signal, such as by using a heart sound detector to detect at leastone parameter indicative of an atrial filling pressure of the heartusing the heart sound signal. The system also includes means forcomparing the at least one parameter to a threshold, such as by using aprocessor to compare the at least one parameter to the threshold.

In Example 16, a method includes sensing a heart sound signal of a heartusing an implanted heart sound sensor. The method also includesdetecting at least one parameter indicative of an atrial fillingpressure of the heart using the heart sound signal. The method alsoincludes comparing the at least one parameter to a threshold.

In Example 17, the method of Example 16 optionally includes detectingthe at least one parameter indicative of an atrial filling pressureincludes detecting at least one parameter indicative of a left atrialfilling pressure.

In Example 18, the method of Examples 16-17 optionally includesdetecting the at least one parameter includes detecting at least onemeasurement, feature, characteristic, computation, or interval of theheart sound signal.

In Example 19, the method of Examples 16-18optionally includes detectingthe at least one measurement, feature, characteristic, computation, orinterval of the heart sound signal includes detecting at least one of anamplitude of a third heart sound (S3), a split second heart sound (S2)time interval, an S2-S3 time interval, and a normalized amplitude orinterval of at least one measurement, feature, or characteristic of theheart sound signal.

In Example 20, the method of Examples 16-19optionally includes sensing acardiac signal of the heart using an implanted cardiac sensor. Thedetecting the at least one parameter of Examples 16-19 also optionallyincludes using the heart sound signal and the cardiac signal.

In Example 21, the detecting the at least one parameter of Examples16-20 optionally includes detecting at least one measurement, feature,characteristic, computation, or interval between at least one cardiacsignal feature and at least one heart sound signal feature.

In Example 22, the detecting the at least one parameter of Examples16-21 optionally includes detecting at least one systolic time interval(STI).

In Example 23, the comparing the at least one parameter to a thresholdof Examples 16-22 optionally includes comparing the at least oneparameter to a predefined threshold.

In Example 24, the comparing the at least one parameter to a thresholdof Examples 16-23 optionally includes comparing the at least oneparameter to an absolute threshold.

In Example 25, the method of Examples 16-24 optionally includes sensinga posture signal using a posture sensor. The comparing the at least oneparameter to a threshold of Examples 16-24 also optionally includesusing the posture signal.

In Example 26, the method of Examples 16-25 optionally includesgenerating an alert using the at least one parameter.

In Example 27, the generating an alert of Examples 16-26 optionallyincludes generating an alert with a predefined specificity.

In Example 28, the generating an alert with a predefined specificity ofExamples 16-27 optionally includes generating an alert with a predefinedspecificity of at least 85%.

In Example 29, the generating an alert with a predefined specificity ofExamples 16-28 optionally includes generating an alert with a predefinedspecificity of at least 90%.

This overview is intended to provide an overview of the subject matterof the present patent application. It is not intended to provide anexclusive or exhaustive explanation of the invention. The detaileddescription is included to provide further information about the subjectmatter of the present patent application.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings, which are not necessarily drawn to scale, like numeralsdescribe substantially similar components throughout the several views.Like numerals having different letter suffixes represent differentinstances of substantially similar components. The drawings illustrategenerally, by way of example, but not by way of limitation, variousembodiments discussed in the present document.

FIG. 1 is a block diagram illustrating an embodiment of a heart-soundbased hemodynamics monitoring and therapy control system.

FIG. 2 is an illustration of an embodiment of a method for detectingselected heart sounds.

FIG. 3 is a block diagram illustrating an embodiment of a measurementmodule of the system of FIG. 1.

FIG. 4 is a flow chart illustrating an embodiment of a method forhemodynamics monitoring and therapy control using the system of FIG. 1.

FIG. 5 is an illustration of an embodiment of portions of a cardiacrhythm management system incorporating heart-sound based hemodynamicsmonitoring and therapy control and portions of an environment in whichit is used.

FIG. 6 is a block diagram illustrating a specific embodiment of portionsof the cardiac rhythm management system of FIG. 5.

FIG. 7 is a block diagram illustrating another specific embodiment ofportions of the cardiac rhythm management system of FIG. 5.

FIG. 8 illustrates generally an embodiment of a system including animplantable medical device, which includes a heart sound sensor, a heartsound detector, and a processor.

FIG. 9 illustrates generally an embodiment of a system including animplantable medical device, which includes a heart sound sensor, a heartsound detector, a cardiac sensor, and a processor.

FIG. 10 illustrates generally an embodiment of a system including aprocessor and a posture sensor.

FIG. 11 illustrates generally an embodiment of a system including aprocessor and an alert module.

FIG. 12 illustrates generally an embodiment of a relationship betweenleft atrial pressure (LAP) and the amplitude of the third heart sound(S3).

FIG. 13 illustrates generally an embodiment of a method includingsensing a heart sound signal, detecting at least one parameterindicative of an atrial filling pressure, and generating an alert whenthe at least one parameter indicative of an atrial filling pressurecrosses a threshold.

FIG. 14 illustrates generally an embodiment of a method includingsensing a heart sound signal, detecting at least one parameterindicative of an atrial filling pressure, sensing a posture signal, andgenerating an alert when the at least one parameter indicative of anatrial filling pressure crosses a threshold.

FIG. 15 illustrates generally and embodiment of a method includingsensing a heart sound signal, sensing a cardiac signal, detecting atleast one parameter indicative of an atrial filling pressure, andgenerating an alert when the at least one parameter indicative of anatrial filling pressure crosses a threshold.

DETAILED DESCRIPTION

The following detailed description includes references to theaccompanying drawings, which form a part of the detailed description.The drawings show, by way of illustration, specific embodiments in whichthe invention may be practiced. These embodiments, which are alsoreferred to herein as “examples,” are described in enough detail toenable those skilled in the art to practice the invention. Theembodiments may be combined, other embodiments may be utilized, orstructural, logical and electrical changes may be made without departingfrom the scope of the present invention. The following detaileddescription is, therefore, not to be taken in a limiting sense, and thescope of the present invention is defined by the appended claims andtheir equivalents.

In this document, the terms “a” or “an” are used, as is common in patentdocuments, to include one or more than one. In this document, the term“or” is used to refer to a nonexclusive or, unless otherwise indicated.Furthermore, all publications, patents, and patent documents referred toin this document are incorporated by reference herein in their entirety,as though individually incorporated by reference. In the event ofinconsistent usages between this document and those documents soincorporated by reference, the usage in the incorporated reference(s)should be considered supplementary to that of this document; forirreconcilable inconsistencies, the usage in this document controls.

This document discusses, among other things, a system monitoring heartsounds indicative of a heart's mechanical events related to the heart'spumping functions and hemodynamic performance to allow, among otherthings, diagnosis of cardiac conditions and selection of therapiestreating the cardiac conditions. The cardiac rhythm management systemsinclude systems having, for example, pacemakers,cardioverter/defibrillators, pacemaker/defibrillators, and cardiacresynchronization therapy (CRT) devices. One specific example of acardiac rhythm management system that monitors and analyses heart soundsis described in co-pending, commonly assigned Siejko et al. U.S. patentapplication Ser. No. 10/307,896, entitled “PHONOCARDIOGRAPHICIMAGE-BASED ATRIOVENTRICULAR DELAY OPTIMIZATION,” filed Dec. 2, 2002,which is hereby incorporated by reference in its entirety. However, itis to be understood that the present methods and apparatuses may beemployed in other types of medical devices, including, but not beinglimited to, drug delivery systems and various types of cardiacmonitoring devices.

Known and studied heart sounds include the “first heart sound” or S1,the “second heart sound” or S2, the “third heart sound” or S3, the“fourth heart sound” or S4, and their various sub-components. S1 isknown to be indicative of, among other things, mitral valve closure,tricuspid valve closure, and aortic valve opening. S2 is known to beindicative of, among other things, aortic valve closure and pulmonaryvalve closure. S3 is known to be a ventricular diastolic filling soundoften indicative of certain pathological conditions including heartfailure. S4 is known to be a ventricular diastolic filling soundresulted from atrial contraction and is usually indicative ofpathological conditions. The term “heart sound” hereinafter refers toany heart sound (e.g., S1) and any components thereof (e.g., M1component of S1, indicative of Mitral valve closure).

Throughout this document, “heart sound” includes audible and inaudiblemechanical vibrations caused by cardiac activity that can be sensed withan accelerometer. Accordingly, the scope of “acoustic energy” in thisdocument extends to energies associated with such mechanical vibrations.

Throughout this document, “user” refers to a physician or othercaregiver who examines and/or treats a patient using one or more of themethods and apparatuses reported in the present document. Unless notedotherwise, S1, S2, S3, and S4 refer to the first, second, third, andfourth heart sounds, respectively, as a heart sound type, or as one ormore occurrences of the corresponding type heart sounds, depending onthe context.

FIG. 1 is a block diagram illustrating an embodiment of a heart-soundbased hemodynamics monitoring and therapy control system 100. System 100includes, among other things, an acoustic sensor 110, a sensor interfacemodule 120, a cardiac sensing circuit 112, a heart sound detector 130, aparameter generator 140, a data acquisition timer 118, a parameterprocessor 160, and a therapy circuit 170. In one embodiment, system 100is a totally implantable system adapted to be implanted into a patient.In an alternative embodiment, system 100 is an external system that doesnot include any implantable component. In another alternativeembodiment, system 100 includes both implantable and externalcomponents.

Acoustic sensor 110 senses an acoustic energy or mechanical vibrationenergy related to cardiac mechanical activities and converts theacoustic energy to an acoustic sensor signal indicative of heart sounds.The acoustic sensor signal is an electrical signal indicative of timing,strength, and frequency characteristics related to the heart sounds.Acoustic sensor 110 is disposed in a heart, or near the heart in alocation where the acoustic energy related to the cardiac mechanicalactivities can be sensed. In one embodiment, acoustic sensor 110includes an accelerometer disposed in or near a heart. In anotherembodiment, acoustic sensor 110 includes a microphone disposed in ornear a heart.

Sensor interface module 120 has a signal input connected to the outputof acoustic sensor 110 to receive the acoustic sensor signal. Itprocesses the acoustic sensor signal to prepare for detection ofselected type heart sounds. The selected type heart sounds are heartsounds selected for a purpose of monitoring a patient's hemodynamicperformance indicated by the measurable characteristics of these heartsounds. In one specific embodiment, the selected type heart soundsincludes S3 and S4, which are indicative of ventricular diastolichemodynamic performance. Sensor interface module includes a signalconditioning circuit 122, a digitizer 124, and a digital filter 126.Signal conditioning circuit 122 receives the acoustic sensor signal asan analog signal from acoustic sensor 110, and performs initialconditioning of the acoustic sensor signal. In one embodiment, signalconditioning circuit 122 improves the signal-to-noise ratio of theacoustic sensor signal. It includes an amplifier and a filter to amplifythe acoustic sensor signal while reducing the noise therein. In oneembodiment, the filter is an analog filter that substantially reducesamplitudes of noises that are not within the frequency spectrum of theselected type heart sounds. In another embodiment, the filtersubstantially reduces amplitudes of noises as well as components of theacoustic sensor signal that are outside of the frequency range of theselected type heart sounds. Digitizer 124 digitizes the filteredacoustic sensor signal by sampling it at a predetermined rate. In oneembodiment, the sampling rate is programmable and determined based onknown frequency characteristics of the heart sounds to be detected. Inone embodiment, digitizer 124 samples the acoustic sensor signal onlyduring predetermined periods of time where the selected type heartsounds are most likely to be present. This saves electrical energyrequired for processing the acoustic sensor signal and/or allows ahigher resolution of the digitized acoustic sensor signal withoutsubstantially increasing the electrical energy required for processing.Energy conservation is of particular importance when system 100 is atotally implantable system or includes implantable components. Digitalfilter 126 substantially reduces amplitudes for all components of theacoustic sensor signal except the selected type heart sounds, which areto be detected by heart sound detector 130, thereby enhancing theindications of the selected type heart sounds. In one embodiment,digital filter 126 includes a band-pass filter having cutoff frequenciesdetermined based on the frequency spectrum of the selected type heartsounds. It is to be understood, however, that the cutoff frequencies aredependent on the purpose of detection and need not cover exactly theknown spectrum of particular heart sounds. In one specific embodiment,digital filter 126 is band-pass filter having a low cutoff frequency inthe range of 5 to 20 Hz and a high cutoff frequency in the range of 30to 120 Hz selected for the purpose of detecting S3 and S4. One exampleof a suitable pass band for digital filter 126 for detection of S3 andS4 for monitoring ventricular diastolic hemodynamics includes a lowcutoff frequency of 10 Hz and a high cutoff frequency of 60 Hz. In onespecific embodiment, digital filter 126 is an envelope detector typefilter. In one embodiment, digital filter 126 is a programmable digitalfilter in which at least one of the cutoff frequencies is programmable.This allows a dynamic selection of heart sounds for detection without aneed for additional circuitry.

Cardiac sensing circuit 112 senses at least one cardiac signalindicative of cardiac electrical events that are needed for detectionand measurements related to the heart sounds and/or their components. Inone embodiment, the cardiac signal includes a surface ECG signal. Inanother embodiment, the cardiac signal includes an intracardiac ECGsignal that is also referred to as an electrogram. Cardiac sensingcircuit 112 includes a sensing amplifier to sense the cardiac signal, acardiac events detector to detect the cardiac electrical events, and anevent marker generator to label each detected cardiac electrical eventwith an event marker indicative of the timing and type of the detectedcardiac electrical event. The detected electrical events include, by notlimited to, selected atrial and ventricular contractions. The atrial andventricular contractions include spontaneous contractions andartificially stimulated contractions.

Heart sound detector 130 detects the selected type heart sounds. In oneembodiment, heart sound detector 130 detects the selected type heartsounds based on the acoustic sensor signal. In another embodiment, heartsound detector 130 detects the selected type heart sounds based on theacoustic sensor signal and the cardiac signal sensed by cardiac sensingcircuit 112. In one embodiment, heart sound detector includes a gatingmodule 132 and a detection module 134. Gating module 132 receives theacoustic sensor signal from sensor interface module 120 and the cardiacsignal from cardiac sensing circuit 112. In one embodiment, the cardiacsignal received by gating module 132 includes event makers representingthe detected cardiac electrical events that allow or facilitatedetection of the selected type heart sounds. Gating module 132 generatesheart sound detection windows each timed for detection of one of theselected type heart sounds based on a time of occurrence of one ofcardiac electrical events. FIG. 2 illustrates, by way of example, butnot by way of limitation, a heart sound detection window. As illustratedin FIG. 2, a cardiac signal 200 indicates a heart contraction 202. Anevent marker signal 210, which is a representation of cardiac signal200, includes an event marker 212 representing heart contraction 202. Anacoustic sensor signal 230, simultaneously recorded with cardiac signal200, includes an indication of a heart sound 235. Based on availablemedical knowledge including statistical information available for anindividual patient, heart sound 235 is substantially probable to occurwithin a time period T2 which starts after a time period T1 triggered byevent marker 212 representing heart contraction 202. Thus, gating module132 generates a heart sound detection window having a duration of T2 atthe end of T1 following each heart contraction used for detection of theselected type heart sounds. In another embodiment, another heart sound(of a different type than the selected type) substitutes heartcontraction 202 to trigger T1, and gating module 132 generates the heartsound detection window T2 at the end of T1 following each heart soundused for detection of the selected type heart sounds. In one embodiment,the heart sound detection windows are used to conserve energy and/orcomputational resources of system 100 by limiting the need for detectionand subsequent computations to periods within the heart sound detectionwindows. In another embodiment, it is difficult or practicallyimpossible to differentiate one type of the heart sounds from another byamplitude or frequency spectrum. This necessitates a method of detectionthat is not based on the amplitude or frequency spectrum of the selectedtype heart sounds. One feasible method includes the use one or moreheart sound detection windows each corresponding to one or more types ofheart sounds, thus allowing detections of heart sounds based on theirpredicted ranges of time of occurrence. Durations of the windows aredetermined based on an empirical study on the timing of each type ofheart sounds relative to a type of cardiac. Heart sound detector 134detects the selected type heart sounds. In one embodiment, heart sounddetector 134 detects the selected type heart sounds within the one ormore heart sound detection windows. In one embodiment, heart sounddetector 134 includes one or more comparators to detect the selectedtype heart sounds by comparing the amplitude of the acoustic sensorsignal during the one or more heart sound detection windows with one ormore predetermined detection thresholds.

Following the detections of the selected type heart sounds by heartsound detector 130, parameter generator 140 makes measurements togenerate parameter values of at least one predetermined parameterrelated to the detected heart sounds. In one embodiment, such aparameter value is measured from one detected heart sound. In anotherembodiment, the parameter value is calculated based on measurement ofseveral detected heart sounds of the same type. The parameter valuesindicate the patient's hemodynamic performance, either directly or afterfurther processing as discussed below. Parameter generator 140 includesa measurement module 150 to make measurements on the acoustic sensorsignal. The measurements are timed with the detections of the selectedtype heart sounds. In one embodiment, measurement module 150 receivesthe acoustic sensor signal from heart sound detector 130 and the cardiacsignal from cardiac sensing circuit 112. FIG. 3 is a block diagram thatillustrates, by way of example, but not by way of limitation, componentsof measurement module 150. As illustrated in FIG. 3, measurement module150 includes a strength detector 351, a relative strength detector 352,a duration timer 353, an electromechanical interval timer 354, amechanical interval timer 355, and a frequency analyzer 356. Strengthdetector 351 measures amplitudes each associated with a detected heartsound. Relative strength detector 352 determines differences eachbetween amplitudes associated with two detected heart sounds. Durationtimer 353 measures durations each associated with a detected heartsound. Electromechanical interval timer 354 measures electromechanicaltime intervals each between a detected heart sound and a cardiacelectrical event detected from the cardiac signal. Mechanical intervaltime 355 measures mechanical time intervals each between two detectedheart sounds. Frequency analyzer 356 computes fundamental and/orharmonic frequencies each associated with a detected heart sound. In oneembodiment, measurement module 150 calculate one or more parametervalues each based on several values of a predetermined parametermeasured by one of the components of measurement module 150. In onespecific embodiment, measurement module 150 calculates the one or moreparameter values each being an average of the several values of thepredetermined parameter. Because of the nature and property of theacoustic sensor, the parameter values output from measurement module 150may includes those affected by background interference. For example,when the acoustic sensor is an accelerometer, the acoustic sensor signalmay indicate a patient's physical activities in addition to the heartsounds. When the acoustic sensor is a microphone, the acoustic sensorsignal may indicate talking and other environment sounds in addition tothe heart sounds. Thus, in one embodiment, parameter generator 140includes a screening module 144 to exclude parameter values resultedfrom measurements performed when a background noise level exceeds apredetermined threshold. In one embodiment, a noise monitoring module142 measures the background noise level. In one specific embodiment,noise monitoring module 142 includes an activity sensor that senses apatient's physical activities and an activity sensor interface module toconvert the physical activities to the background noise level. Inanother specific embodiment, noise monitoring module includes a furthersensor interface module coupled to acoustic sensor 110, which senses thepatient's physical activities in addition to the acoustic energy relatedto the patient's cardiac mechanical activities. When acoustic sensor 110includes an accelerometer, the further sensor interface module includesan activity level detector to produce the background noise level signalindicative of the patient's physical activities. The activity level asindicated by the acoustic sensor signal has a distinctively higheramplitude than the heart sounds. Thus, the activity level detectordistinguishes the patient's physical activities from the heart sounds byusing a predetermined activity level threshold. In one embodiment,parameter generator 140 includes a memory circuit 146 to store theparameter values generated by measurement module 150. In anotherembodiment, memory 146 stores only parameters screened by screeningmodule 144.

Data acquisition enabler 118 controls the timing of overall dataacquisition by timing the enablement of selected system componentsincluding at least one or more of acoustic sensor 110, sensor interfacemodule 120, cardiac sensing circuit 112, heart sound detector 130, andparameter generator 140. In one embodiment, data acquisition enabler 118enables the selected system components in response to an externalcommand, such as given by the user. In another embodiment, dataacquisition enabler 118 includes a data acquisition timer to enable theselected system components on a predetermined schedule. In one specificembodiment, the data acquisition timer enables the selected systemcomponents on a predetermined periodic basis. In another specificembodiment, if parameter generator 140 is unable to generate requiredparameter values on the predetermined schedule, for example, because thebackground noises exceeds the predetermined level when the selectedsystem components are enabled, data acquisition enabler 118 modifies thepredetermined schedule by introducing at least one delay to ensure thatall the desired parameter values are obtained.

Parameter processor 160 processes the parameter values received fromparameter generator 140. In one embodiment, parameter processor 160includes a statistical processor 162, a trending analyzer 164, and analert signal generator 166. Statistical processor 162 analyzes theparameter values generated by parameter generator 140 for apredetermined period of time. Trending analyzer 164 produces at leastone trend related to the selected type heart sounds. The trend is ahemodynamic performance trend indicative of one or more cardiacconditions. In one embodiment, the trend is a plot of parameter valuesof one selected parameter related to the detected heart sounds over apredetermined period of time. In another embodiment, the trend is a plotof values derived for the parameter values as a result of thestatistical process over the predetermined period of time. Alert signalgenerator 166 generates an alert signal indicative of a presence of theone or more cardiac conditions indicated by the at least one trend. Inone embodiment, alert signal generator 166 includes a comparator. Thecomparator has a first input to receive the at least one trend, a secondinput representative of a predetermined threshold level, and an outputindicative of the presence of the one or more clinical conditions whenthe at least one trend exceeds the predetermined threshold level. In onefurther embodiment, alert signal generator 166 includes a thresholdgenerator that generates an adaptive threshold level based on at leastone previously produced trend, such that the predetermined threshold isdynamically adjustable based on the patient's changing cardiacconditions.

Therapy circuit 170 includes, by way of example, but not by way oflimitation, one or more of a pacing circuit, a defibrillation circuit, acardiac resynchronization circuit, and a drug delivery circuit. Itincludes a therapy controller to execute a predetermined therapyalgorithm that times therapy deliveries based on the processed cardiacsignal and acoustic sensor signal. In one embodiment, the therapycontroller receives at least one of selected parameter values generatedby parameter generator 140, the at least one trend generated by trendinganalyzer 164, and the alert signal generated by alert signal generator166, based on which it produces or adjusts one or more therapyparameters.

FIG. 4 is a flow chart illustrating an embodiment of a method forhemodynamics monitoring and therapy control using system 100. At 400,data acquisition for the hemodynamics monitoring and therapy controlbegins. In one embodiment, the data acquisition begins as system 100 isactivated. In one embodiment, the data acquisition begins in response toa user command. In another embodiment, the data acquisition begins at apredetermined time or upon a predetermined triggering event. In oneembodiment, the date acquisition lasts for a predetermined durationafter it begins. In one specific embodiment, the data acquisition beginson a predetermined periodic basis and lasts for a predeterminedduration.

At 402, acoustic sensor 110 senses the acoustic energy related tocardiac mechanical activities and converts the acoustic energy to anacoustic sensor signal indicative heart sounds. In one embodiment,acoustic sensor 110 senses an acceleration indicative of the acousticenergy.

At 410, sensor interface module 410 processes the acoustic sensor signalto prepare for heart sound detection. In one embodiment, the acousticsensor signal is amplified and filtered to increase its signal-to-noiseratio. Then, the acoustic sensor signal is digitized to the form ofbinary data. The digitized acoustic sensor signal is filtered to enhanceindications of the selected type heart sounds. In one embodiment, thedigitized acoustic sensor signal is filtered with at least one cutofffrequency determined based on the frequency spectrum of the selectedtype heart sounds.

At 420, heart sound detector 130 generates heart sound detection windowseach timed for detecting one of the selected type heart sounds. Theheart sound detection windows are each triggered by one of selectedcardiac electrical events detected from the cardiac signal sensed at404. In one embodiment, the selected cardiac electrical events includeat least one of spontaneous or artificially stimulated atrial andventricular contractions. In one embodiment, the selected cardiacelectrical events are each represented by a predetermined event marker.In one specific embodiment, At 425, the selected type heart sounds aredetected. In one embodiment, each of the selected type heart sounds isdetected when the amplitude of the acoustic sensor signal exceeds apredetermined threshold level.

At 430, parameter generator 140 generates the parameter values of atleast one parameter related to the detected heart sounds based on theacoustic sensor signal produced at 400 and/or the cardiac signal sensedat 404. Such parameter values include, by way of example, but not by wayof limitation, one or more of (i) an amplitude associated with one orone selected type of the selected type heart sounds; (ii) a relativestrength being differences between amplitudes associated with two or twoselected types of the selected type heart sounds; (iii) a durationassociated with one or one selected type of the selected type heartsounds; (iv) an electromechanical time intervals between one or oneselected type of the selected type heart sounds and one or one type ofselected type cardiac electrical events; (v) a mechanical time intervalbetween two or two selected types of the selected type heart sounds; and(vi) a fundamental or harmonic frequency associated with one or oneselected type of the selected type heart sounds. In one embodiment,parameter values related to S3 and/or S4 are measured and/or calculatedfor the purpose of monitoring ventricular diastolic hemodynamicperformance. The parameter values of one or more of the followingparameters are generated: (i) peak amplitude of S3; (ii) time of onsetof S3 relative to onset of S2; (iii) duration of S3; (iv) fundamentalfrequency if S3; (v) time of occurrence of S3 relative to thesubsequently adjacent atrial contraction; (vi) peak amplitude of S4;(vii) time interval between atrial contraction and the subsequentlyadjacent S4; (viii) fundamental frequency of S4; (ix) duration of S4;(x) time of occurrence of S4 relative to the subsequently adjacentventricular contraction; and (xi) amplitude of S4 relative to amplitudeof S3. In one embodiment, parameter generator 140 screens out noisyvalues of the parameter values measured at 435. Such noisy valuesinclude parameter values measured when the background noise levelexceeds a predetermined threshold. In one embodiment, the patient'sphysical activities are sensed at 406 to produce an activity levelsignal indicative of the background noise level. In one specificembodiment, the activity level signal is derived from the same acousticsensor signal from which the selected type heart sounds are detected.This is possible because the patient's physical activities are typicallyindicated with amplitudes that are distinctively higher than theamplitudes of the selected type heart sounds.

At 440, the parameter values are stored in memory circuit 146 or otherstorage medium. In one embodiment, system 1 00 uses the parameter valuesdirectly to control delivery of at least one therapy with at least onetherapy parameter being a function of the parameter values. In anotherembodiment, the parameter values are further processed and analyzed bysystem 100 for monitoring, diagnosis, and/or therapy control purposes.In yet another embodiment, the stored parameter values are transferredto another system, such as a computer separated from system 100, forfurther processing and/or analysis.

At 450, parameter processor 160 statistically processes the parametervalues. The statistical process includes analyzing the parameter valuesof the at least one parameter related to the detected heart sounds inrelation to historical values of that parameter measured during apredetermined period of time. The outcome of the statistical processreveals changes in cardiac conditions reflected in the characteristicsof the selected type heart sounds. In one embodiment, the outcome of thestatistical process reveals changes in ventricular diastolic filingpatterns during the predetermined period of time. In one specificembodiment, the predetermined period of time ranges from 1 day to 3months.

At 460, parameter processor 160 produces at least one hemodynamicperformance trend related to the selected type heart sounds. In oneembodiment, parameter processor 160 produces the at least one trendbased on the outcome of the statistical analysis. In one embodiment, oneor more trends quantitatively present one or more ventricular diastolicfiling pattern changes during a predetermined duration. In oneembodiment, parameter processor 160 plots the parameter values of the atleast one parameter related to the detected heart sounds versus time. Inanother embodiment, parameter processor 160 statistically processes theparameter values of the at least one parameter related to the detectedheart sounds and plots the result. At 465, the one or more trends areanalyzed for indication of cardiac conditions. In one embodiment, thevalues of each trend are compared to a predetermined threshold level,and a predefined cardiac condition is indicated when any value exceedsthe predetermined threshold level. In one embodiment, the predeterminedthreshold level is determined based on at least one previously producedtrend.

At 475, an alert signal is generated when a cardiac condition isindicated by the at least one hemodynamic performance trend at 470. Thealert signal notifies the user of the cardiac condition that may needmedical attention. In one embodiment, the cardiac condition requiresdelivery of a therapy. In another embodiment, the alert signal indicatesa need for changing one or more therapy parameters.

In one embodiment, a therapy is delivered in response to the alertsignal at 480. The therapy includes one or more of, for example, apacing therapy, a defibrillation therapy, a cardiac resynchronizationtherapy, any other electrical stimulation therapy, and a drug therapy.The type of the therapy as therapy parameters are determined based onthe at least one trend and/or selected values of the at least oneparameter related to the detected heart sounds. In one specificembodiment, therapy circuit 170 delivers the therapy. In anotherembodiment, one or more therapy parameters are adjusted in response tothe alert signal, and the new therapy parameters are determined based onthe at least one trend and/or the selected values of the at least oneparameter related to the detected heart sounds. In an alternativeembodiment, the therapy delivery or the therapy parameter adjustmentsare not dependent on the alert signal. The at least one trend and/or theselected values of the at least one parameter related to the detectedheart sounds directly determine the need for the therapy delivery or thetherapy parameter adjustments.

Many embodiments combining the present method with available medicalknowledge will be apparent to those of skill in the art. In one example,the fundamental frequency (also referred to as the pitch) of S3 iscorrelated to the stiffness of the left ventricular wall during therapid filling phase of diastole. The wall stiffness is proportional todiastolic pressure in the left ventricle and to the thickness of theleft ventricular wall. Therefore, an increase in the pitch of S3 is usedto indicate one or more of an elevated left ventricular filling pressureand a thickened left ventricular wall. The elevation of the leftventricular filling pressure and/or the increase of the left ventricularwall thickness may reach a degree, represented by predeterminedthresholds of S3 fundamental frequency, that requires an application ofadjustment of a therapy. In another example, the amplitude of S3 isdirectly related to the rate of deceleration of blood flow into the leftventricle during the rapid filling phase of diastole. An increase inamplitude of S3 can be used to indicate an elevation of left atrialfilling pressure, an increase in stiffness of the left ventricle, orboth, which represent a restrictive filling pattern associated withheart failure. Therefore, the trend of S3 amplitude is useful inmonitoring cardiac mechanical properties related to heart failure. Inyet another example, the elevated filling pressures cause pulmonaryedema. Thus, a physician determines the need of a drug therapy torelieve the elevated pressures based on one or more trends of parametersrelated to S3. These are a few examples, among many possibleembodiments, illustrating how system 100 is used. In general, trends ofany of the measured parameter values can be used individually, jointly,and/or in combination with other trends related to cardiac functions.

FIG. 5 is an illustration of an embodiment of portions of a cardiacrhythm management system 599 and portions of an environment in which itis used. System 599 incorporates a heart-sound based hemodynamicsmonitoring and therapy control system such as system 100. In oneembodiment, cardiac rhythm management system 599 includes an implantedsystem 505, an external system 580, and a telemetry link 570 providingfor communication between implanted system 505 and external system 580.Implanted system 505 includes an implanted device 506 and a lead system508. Implanted device 506 is implanted within a patient's body 502 andcoupled to the patient's heart 501 via lead system 508. Examples ofimplanted device 506 include pacemakers, cardioverter/defibrillators,pacemaker/defibrillators, cardiac resynchronization devices, and drugdelivery devices. External system 580 is a patient management systemincluding an external device 585 in proximity of implanted device 502, aremote device 595 in a relatively distant location, and atelecommunication system 590 linking external device 585 and remotedevice 595. An example of such a patient management system is discussedin Hatlestad et al., “ADVANCED PATIENT MANAGEMENT FOR DEFINING,IDENTIFYING AND USING PREDETERMINED HEALTH-RELATED EVENTS,” applicationSer, No. 10/323,604, filed on Dec. 18, 2002, assigned to CardiacPacemakers, Inc., the specification of which is incorporated herein byreference in its entirety. In one embodiment, telemetry link 570 is aninductive telemetry link. In an alternative embodiment, telemetry link570 is a far-field radio-frequency telemetry link. In one embodiment,telemetry link 570 provides for data transmission from implanted device506 to external device 585. This may include, for example, transmittingreal-time physiological data acquired by implanted device 506,extracting physiological data acquired by and stored in implanted device506, extracting therapy history data stored in implanted device 506, andextracting data indicating an operational status of implanted device 506(e.g., battery status and lead impedance). In a further embodiment,telemetry link 570 provides for data transmission from external device585 to implanted device 506. This may include, for example, programmingimplanted device 506 to acquire physiological data, programmingimplanted device 506 to perform at least one self-diagnostic test (suchas for a device operational status), and programming implanted device506 to deliver at least one therapy.

In one embodiment, programming implanted device 506 includes sendingtherapy parameters to implantable device 506. The therapy parametersprovide an improved hemodynamic performance for a patient by deliveringcardiac pacing pulses to the patient's heart. In one embodiment, thetherapy parameters providing for the improved hemodynamic performanceare determined by monitoring one or more ventricular diastolichemodynamics as indicated by parameters related to heart sounds such asS3 and S4. Such parameters indicate the heart's mechanical activitiesand electromechanical association. In one specific embodiment, theacquisition of values of such parameters, the processing of theparameter values, and the subsequent determination of the therapyparameters are performed by system 100, as discussed above withreference to FIGS. 1-3.

FIG. 6 is a block diagram illustrating a specific embodiment of portionsof cardiac rhythm management system 599. In this embodiment, system 100is substantially included within implanted device 506. System 100includes, as discussed above with reference to FIG. 1, acoustic sensor110, sensor interface module 120, cardiac sensing circuit 112, heartsound detector 130, parameter generator 140, data acquisition timer 118,parameter processor 160, and therapy circuit 170. Implanted device 506also includes, among other things, an implant telemetry module 672 andan implant antenna 674 to provide implanted device 506 with telemetrycapability allowing it to communicate with external system 580 viatelemetry link 570. In one embodiment, therapy circuit 170 includes atherapy controller that executes a predetermined therapy controlalgorithm to determine whether to deliver a therapy or adjust one ormore therapy parameters based on the one or more of the heart sound-related parameter values generated by parameter generator 140 and trendsand alert signal generated by parameter processor 160.

External system 580 includes, among other things, an external antenna676, an external telemetry module 678, a controller 682, and a userinterface 684. In one embodiment, external telemetry module 678 andexternal antenna 676 are included in external device 585 to provideexternal system 580 with capability of communicating with implanteddevice 506 through telemetry link 570 and external device 585.Controller 682 controls telemetry operation of external system 580,processes signals received from implanted device 506 for presentation onuser interface 684, and processes user commands entered through userinterface 684 for transmission to implanted device 506. In oneembodiment, one or more of the heart-sound related parameter values,trends, and alert signal, as discussed above, are acquired by system 100and telemetered to external system 580 via telemetry link 570.Controller 682 executes a predetermined therapy control algorithm todetermine whether to deliver a therapy or adjust one or more therapyparameters based on the one or more of the heart sound-related parametervalues, trends, and alert signal.

In one embodiment, system 100 is completely within a hermetically sealedcan that houses at least portions of implanted device 506. Housingacoustic sensor 110 in the can has the advantage of minimizing thebackground noise associated with physical movements of the sensor,especially when acoustic sensor 110 includes an accelerometer. Inanother embodiment, acoustic sensor 110 is attached to a lead of leadsystem 508. This allows disposition of acoustic sensor 110 in or nearheart 501 such that it is near the mechanical activities being thesources of the heart sounds of interest.

To include substantially the whole system 100 within implanted device506 provides for the advantage of a self-contained implantable cardiacrhythm management system incorporating heart-sound based therapycontrol. In one embodiment, the heart-sound based therapy control usingsystem 100 is able to function without telemetry link 570, for example,when the patient is outside the range of the telemetry communication.Implanted device 506 determines, without the intervention of the user orcontroller 682, whether to deliver a therapy or adjust one or moretherapy parameters based on the one or more of the parameter values,trends, and alert signal generated within itself by system 100.

FIG. 7 is a block diagram illustrating another specific embodiment ofportions of cardiac rhythm management system 599. In this embodiment,system 100 is partially included within implantable device 506 andpartially included in external system 580. In one specific embodiment,parameter processor 160 is within external system 580, and the remainingcomponents of system 100 are within implanted device 506. Parametervalues generated by parameter generator 140 are telemetered to externalsystem 580 via telemetry link 570 for further processing by parameterprocessor 160. In one embodiment, parameter processor 160 is included inexternal device 585. In an alternative embodiment, parameter processor160 is included in remote device 595.

In one embodiment, the parameter values are telemetered as they aregenerated. In another embodiment, parameter values are first stored inmemory circuit 146. Data acquisition enabler 118 times transmission ofthe parameter values in response to a command from external device 580or on a predetermined schedule.

To include parameter processor 160 in external system 580 avoids placingthe demand of energy and circuit resources required by parameterprocessor 160 in implanted device 506, which is subject to designrestraints including power and size limitations. The advantages alsoinclude the feasibility of updating parameter processing algorithms usedby parameter processor 160 without the need of replacing implanteddevice 506.

It is to be understood that the above detailed description is intendedto be illustrative, and not restrictive. For example, system 100 may beincorporated into any implanted or external medical device providing forECG and heart sound monitoring. Other embodiments will be apparent tothose of skill in the art upon reading and understanding the abovedescription. The scope of the invention should, therefore, be determinedwith reference to the appended claims, along with the full scope ofequivalents to which such claims are entitled.

OTHER EXAMPLES

Generally, heart sounds, e.g., S3, are correlated to heart function.Typically, heart failure arises when the pumping of the heart iscompromised. As heart failure worsens, for various reasons, the pumpingfunction of the heart typically deteriorates. As the pumping function ofthe heart deteriorates, the demand for blood to the body generallyincreases, typically resulting in an increased left atrial pressure. Asthe demand for blood to the body increases and the pumping function ofthe heart deteriorates, fluid typically builds in the lungs. Generally,as fluid builds in the lungs, the demand for increased blood through theheart increases, also typically resulting in an increased left atrialpressure. Thus, increased atrial pressure, including left atrialpressure, is an indicator of heart failure.

A system and method have been developed to correlate one or more thanone heart sound, e.g., S3, to atrial filling pressure, including leftatrial filling pressure, and provide an alert, such as when high atrialfilling pressure is detected. An increase of S3 amplitude, or anothermeasurement, feature, characteristic, computation, or interval of aheart sound signal, can be used to indicate an elevation of left atrialfilling pressure. Therefore, the trend of S3 amplitude, or value ofanother measurement, feature, characteristic, computation, or intervalof the heart sound signal, is useful in monitoring cardiac mechanicalproperties related to heart failure.

Using one or a combination of a measurement, feature, characteristic,computation, or interval of the heart sound signal, a high fillingpressure can be detected, including a high atrial filling pressure, or ahigh left atrial filling pressure. Using the detected pressure, an alertcan be provided, such as for example when the pressure is detected abovean absolute pressure threshold, e.g., 25 mmHg. Other alerts can also beprovided, such as discussed elsewhere in this document.

FIG. 8 illustrates generally an example of portions of a system 800 thatincludes an implantable medical device 805, which includes a heart soundsensor 810, a heart sound detector 815, and a processor 820. In otherexamples, the heart sound detector 815, or the processor 820, can be animplantable component external to the implantable medical device 805, orcan be an external component.

In this example, the heart sound sensor 810 is configured to sense aheart sound signal of a heart. The heart sound signal of the heart caninclude any signal indicative of a heart sound of the heart.Illustrative examples of heart sounds include one or more than one of anS1 heart sound, an S2 heart sound, an S3 heart sound, an S4 heart sound,a regurgitant heart murmur, a stenotic heart murmur sound, and acoronary vascular blood turbulence sound. The heart sound sensor 810 canbe any device configured to sense the heart sound signal of the heart,e.g., an accelerometer, a microphone, etc. The heart sound sensor 810can transduce the heart sound, such as into an electrical or optical“heart sound” signal that includes information about the sensed heartsound.

In the example of FIG. 8, the heart sound detector 815 is coupled to theheart sound sensor 810. In this example, the heart sound detector 815 isgenerally configured to detect at least one parameter indicative of anatrial filling pressure of the heart using the heart sound signal. In anexample, the at least one parameter indicative of an atrial fillingpressure includes at least one heart sound parameter indicative of anatrial filling pressure.

In this example, the processor 820 is coupled to the heart sounddetector 815. The processor 820 is generally configured to compare theat least one parameter indicative of an atrial filling pressure to athreshold. In certain examples, the threshold can include apopulation-based threshold, a specified threshold, an adjustablethreshold, an absolute threshold, or a permutation or combination of oneor more than one threshold. In certain examples, where the threshold isan adjustable threshold, the adjustable threshold can include anautomatically adjustable threshold, such as by the processor 820 inresponse to other information, e.g., the posture signal, etc., a useradjusted threshold, or a manufacturer adjusted threshold. In an example,the processor 820 compares the at least one parameter to the thresholdto determine if the at least one parameter has crossed or is across thethreshold. In certain examples, the at least one parameter has crossedthe threshold if the at least one parameter is of a level that is equalto or below the threshold, or if the at least one parameter is of alevel that is equal to or above the threshold. In other examples, the atleast one parameter is across the threshold if the at least oneparameter is of a level that is equal to or below the threshold, or ifthe at least one parameter is of a level that is equal to or above thethreshold.

In certain examples, the system 800 can operate in an ongoing fashion(e.g., continuously), the system 800 can operate one or more than onetime during one or more than one time period, e.g., one or more than onetime per hour, one or more than one time per day, etc., or the system800 can operate or cease to operate using a triggering event, includinga user or patient input, or a physiological or other sensor input.

FIG. 9 illustrates generally an example of a system 900 that includes animplantable medical device 805, which includes a heart sound sensor 810,a heart sound detector 815, a processor 820, and a cardiac sensor 825.In other examples, the heart sound detector 815, or the processor 820,can be an implantable component external to the implantable medicaldevice 805, or can be an external component.

In this example, the cardiac sensor 825 is coupled to the heart sounddetector 815. The cardiac sensor is generally configured to sense acardiac signal of the heart. The cardiac signal of the heart can includeany signal indicative of the electrical or mechanical cardiac activityof the heart, e.g., an electrocardiogram (ECG) signal, an impedancesignal, an acceleration signal, etc. The cardiac sensor 825 can includeany device configured to sense the cardiac activity of the heart, e.g.,an intrinsic cardiac signal sensor, such as one or more than oneelectrode or lead to sense one or more than one depolarization, amechanical sensor, such as an impedance sensor or an accelerometer tosense one or more than one contraction.

In the example of FIG. 9, the heart sound detector 815 is configured todetect at least one parameter indicative of an atrial filling pressureof the heart using the heart sound signal and the cardiac signal. In anexample, the heart sound detector 815 receives the heart sound signalfrom the heart sound sensor 810 and receives the cardiac signal from thecardiac sensor 825. In an example, the heart sound detector 815 usesinformation from the cardiac signal, such as to time or gate orotherwise assist detection of at least one heart sound, e.g., S1, S2,etc.

FIG. 10 illustrates generally an example of a system 1000 including aprocessor 820 and a posture sensor 830. In an example, the system 1000includes an implantable medical device 805, which includes the processor820 and the posture sensor 830. In other examples, the processor 820, orthe posture sensor 830, can be an implantable component external to theimplantable medical device, or can be an external component.

In the example of FIG. 10, the posture sensor 830 is coupled to theprocessor 820. The posture sensor 830 is generally configured to sense aposture signal indicative of a posture or an activity level of apatient. In an example, the processor 820 is configured to determine,set, or adjust a threshold using information from the posture sensor830. In another example, the processor 820 is configured to determine oradjust at least one parameter indicative of an atrial filling pressureof a heart using information from the posture sensor 830. In certainexamples, the posture sensor 830 includes at least one of anaccelerometer, a pendulum-type device, a tilt switch, and a pressuresensor, or the posture sensor 830 includes a permutation or combinationof one or more than one of the accelerometer, the pendulum-type device,and the pressure sensor. In an example, the processor 820 can determinethe activity of the patient using the posture sensor 830, e.g., usinginformation from the most current posture signal and at least oneprevious posture signal.

FIG. 11 illustrates generally an example of a system 1100 that includesa processor 820 and an alert module 835. In an example, the system 1100includes an implantable medical device 805, which includes the processor820 or the alert module 835. In other examples, the processor 820, orthe alert module 835, can be an implantable component external to theimplantable medical device, or can be an external component.

In the example of FIG. 11, the alert module 835 is coupled to theprocessor 820. The alert module 835 is generally configured to alert auser or a patient using at least one parameter indicative of an atrialfilling pressure of a heart. In certain examples, the alert module 835is configured to alert the patient, such as by generating a noise or avibration. In other examples, the alert module 835 is configured toalert the user or patient, such as by communicating a notification tothe user or patient, e.g., communicating a notification to the user orpatient directly, or communicating a notification to the user or patientthrough some external device, such as an external programmer. In anexample, the alert module 835 is configured to communicate with a remoteuser interface, such as the LATITUDE configuration. In another example,the alert module 835 is configured to communicate to an external device,e.g., an external repeater, which can be configured to communicate to anexternal repeater. In another example, the external repeater can beconfigured to communicate, such as by an e-mail or other communication,to the user.

FIG. 12 illustrates generally an example of a relationship between leftatrial pressure (LAP) 1205 and the amplitude of the third heart sound(S3) 1210. In an example, a data point 1220 includes an S3 amplitudevalue and an LAP value. As is shown in FIG. 12, generally, as the LAP1205 increases, the S3 amplitude 1210 increases.

In an example, using the data of FIG. 12, an S3 threshold 1215 can beset at 4 mG. In this example, an LAP of 25 mmHg or higher can bedetected with a sensitivity of 71% (5/7) and a specificity of 90%(2/20), or an LAP of 20 mmHG or higher can be detected with asensitivity of 64% (7/11) and a specificity of 100% (0/16). In anotherexample, using the data of FIG. 12, the S3 threshold 1215 can be set at2 mG. In this example, an LAP of 10 mmHg or higher can be detected witha sensitivity of 75% (15/20) and a specificity of 86% (1/7).

FIG. 13 illustrates generally an example of a method 1300 includingsensing a heart sound signal, detecting at least one parameterindicative of an atrial filling pressure, and generating an alert whenthe at least one parameter indicative of an atrial filling pressurecrosses a threshold. In an example, the method 1300 can operate in anongoing or continuous manner, the method 1300 can operate one or morethan one particular time during one or more than one time period, e.g.,one or more than one time per hour, one or more than one time per day,etc., or the method 1300 can operate or cease to operate using atriggering event, including a user or patient input.

At 1305, a heart sound signal is sensed. The heart sound signal caninclude any signal indicative of a heart sound of a heart. In anexample, the heart sound signal can be sensed using the heart soundsensor 810.

At 1310, at least one parameter indicative of an atrial filling pressureis detected. In an example, the at least one parameter indicative of anatrial filling pressure is detected using the heart sound signal.

Generally, the at least one parameter indicative of an atrial fillingpressure can include at least one measurement, feature, characteristic,computation, or interval of the heart sound signal. In certain examples,the at least one measurement, feature, characteristic, computation, orinterval of the heart sound signal includes at least one of an amplitudeof a heart sound, a magnitude of a heart sound, a total energy of aheart sound, an interval between one heart sound feature and anotherheart sound feature, at least one heart sound characteristic normalizedby at least one other heart sound characteristic, etc. (e.g., anamplitude or magnitude of S1, an amplitude or magnitude of S2, anamplitude or magnitude of S3, an amplitude or magnitude of S4, theexistence of a split-S2, a split-S2 time interval, a S1-S2 timeinterval, a S2-S3 time interval, a characteristic of S3 normalized by acharacteristic of S1, etc.).

At 1315, the method 1300 determines if the at least one parameterindicative of an atrial filling pressure has crossed, or is across, thethreshold. In an example, at 1315, the processor 820 determines if theat least one parameter indicative of an atrial filling pressure hascrossed the threshold. In an example, if, at 1315, the at least oneparameter indicative of an atrial filling pressure crosses thethreshold, then an alert is generated at 1320. In another example, if,at 1315, the at least one parameter indicative of an atrial fillingpressure is of a level equal to or above the threshold, then an alert isgenerated at 1320. In another example, if, at 1315, the at least oneparameter indicative of an atrial filling pressure is of a level equalto or below the threshold, then an alert is generated at 1320. Incertain examples, the at least one parameter indicative of an atrialfilling pressure can be across the threshold for a certain duration(e.g., one or more than one cardiac cycle, one or more than one minute,one or more than one hour, one or more than one day, etc.) before thealert module is configured to generate an alert, or the at least oneparameter indicative of an atrial filling pressure can cross thethreshold for a certain duration (e.g., the at least one parametercrosses the threshold one time per day for 3 consecutive days, the atleast one parameter crosses the threshold one time per day for 5consecutive days, etc.) before the alert module is configured togenerate an alert.

Generally, generating an alert using a population-based or absolutethreshold allows the user or the processor 820 to set or adjust thethreshold to detect a condition with a predefined specificity orsensitivity. This method can be advantageous over one that uses athreshold where the patient serves as their own control. In certainexamples, by using a population-based threshold, a condition, e.g., highleft atrial filling pressure, can be detected with a very highspecificity, e.g., 86%, 90%, 100%, etc. Detecting a condition with ahigh specificity is generally advantageous due to a reduction infalse-positives, among other reasons. Conversely, setting or adjustingthe threshold to detect a condition with a high specificity typicallydetects the condition with a lower sensitivity. In the example of FIG.12, setting or adjusting the threshold to detect a condition with aspecificity of 86% detects the condition with a sensitivity of 75%,setting or adjusting the threshold to detect a condition with aspecificity of 90% detects the condition with a sensitivity of 71%, andsetting or adjusting the threshold to detect a condition with aspecificity of 100% detects the condition with a sensitivity of 64%.

In another example, at 1315, if processor 820 determines that the atleast one parameter indicative of an atrial filling pressure has notcrossed the threshold, then an alert is not generated, and the processflow returns to 1305.

FIG. 14 illustrates generally an example of a method 1400 includingsensing a heart sound signal, detecting at least one parameterindicative of an atrial filling pressure, sensing a posture signal, andgenerating an alert when the at least one parameter indicative of anatrial filling pressure crosses a threshold.

At 1405, a heart sound signal is sensed. The heart sound signal caninclude any signal indicative of a heart sound of a heart. In anexample, the heart sound signal can be sensed using the heart soundsensor 810.

At 1410, at least one parameter indicative of an atrial filling pressureis detected. In an example, the at least one parameter indicative of anatrial filling pressure is detected using the heart sound signal. In anexample, the at least one parameter indicative of an atrial fillingpressure is detected using the heart sound detector 815.

At 1411, a posture signal is sensed. The posture signal can include anysignal indicative of a posture or an activity level of a patient.Typically, an atrial filling pressure can be more accurately determined,with a higher sensitivity or with a higher specificity, if the postureor the activity level of the patient is known.

In an example, the threshold can be determined, set, or adjusted usinginformation from the posture signal. Generally, when the patient islying in the supine, recumbent, prone, or other lying position, or whenthe patient is inactive or at rest, there exists less noise in the heartsound signal, and thus, a more accurate heart sound signal can typicallybe sensed. In an example, the threshold can be determined, set, oradjusted using information from the posture signal, e.g., lowering thethreshold during long periods of rest, raising the threshold duringperiods of increased activity, etc.

In another example, the at least one parameter indicative of an atrialfilling pressure can be determined or adjusted using information fromthe posture signal. Generally, heart sound information can be dependentupon patient position. In an example, the heart sound signal or the atleast one parameter indicative of an atrial filling pressure can befiltered, adjusted, or attained using information from the posturesignal.

At 1415, the method 1400 determines if the at least one parameterindicative of an atrial filling pressure has crossed the threshold. Inan example, at 1415, the processor 820 determines if the at least oneparameter indicative of an atrial filling pressure has crossed thethreshold. In an example, if, at 1415, the at least one parameterindicative of an atrial filling pressure crosses the threshold, then, at1420, an alert is generated. In another example, the at least oneparameter indicative of an atrial filling pressure can be across thethreshold for a certain duration (e.g., one or more than one cardiaccycle, one or more than one minute, one or more than one hour, one ormore than one day, etc.) before the alert module is configured togenerate an alert. In yet another example, the at least one parameterindicative of an atrial filling pressure can cross the threshold for acertain duration (e.g., the at least one parameter crosses the thresholdone time per day for 3 consecutive days, the at least one parametercrosses the threshold one time per day for 5 consecutive days, etc.)before the alert module is configured to generate an alert.

In another example, if, at 1415, the at least one parameter indicativeof an atrial filling pressure has not crossed the threshold, then analert is not generated, and the process flow returns to 1405.

FIG. 15 illustrates generally an example of a method 1500 includingsensing a heart sound signal, sensing a cardiac signal, detecting atleast one parameter indicative of an atrial filling pressure, andgenerating an alert when the at least one parameter indicative of anatrial filling pressure crosses a threshold.

At 1505, a heart sound signal is sensed. The heart sound signal caninclude any signal indicative of a heart sound of a heart. In anexample, the heart sound signal can be sensed using the heart soundsensor 810.

At 1506, a cardiac signal is sensed. The cardiac signal can include anysignal indicative of a cardiac signal of the heart. In an example, thecardiac signal can be sensed using the cardiac sensor 825.

At 1510, at least one parameter indicative of an atrial filling pressureis detected. In an example, the at least one parameter indicative of anatrial filling pressure is detected using the heart sound signal and thecardiac signal. In an example, the at least one parameter indicative ofan atrial filling pressure is detected using the heart sound detector815. In another example, the at least one parameter indicative of anatrial filling pressure is detected using the processor 820.

Generally, at 1510, the at least one parameter indicative of an atrialfilling pressure includes at least one measurement, feature,characteristic, computation, or interval between at least one cardiacsignal feature and at least one heart sound signal feature. Typically,the at least one cardiac signal feature can include at least one featureor component of an ECG signal, e.g., at least one component of a P-wave,at least one component of a Q-wave, at least one component of a R-wave,at least one component of a S-wave, at least one component of a T-wave,or any combination or permutation of features or components of the ECGsignal. In certain examples, the at least one measurement, feature,characteristic, computation, or interval between at least one cardiacsignal feature and at least one heart sound signal feature includes asystolic time interval (STI) (e.g., a total electromechanical systole(Q-S2), a pre-ejection phase (PEP), a left-ventricular ejection time(LVET), an isovolumetric contraction time (ICT), an interval between S1and S2 (S1-S2), etc.), a long Q-S1 time interval, a R-S1 time interval,R-S2 interval, etc.

At 1515, the method 1500 determines if the at least one parameterindicative of an atrial filling pressure has crossed the threshold. Inan example, at 1515, the processor 820 determines if the at least oneparameter indicative of an atrial filling pressure has crossed thethreshold. In an example, if, at 1515, the at least one parameterindicative of an atrial filling pressure has crossed the threshold,then, at 1520, an alert is generated. In another example, the at leastone parameter indicative of an atrial filling pressure can be across thethreshold for a certain duration (e.g., one or more than one cardiaccycle, one or more than one minute, one or more than one hour, one ormore than one day, etc.) before the alert module is configured togenerate an alert. In yet another example, the at least one parameterindicative of an atrial filling pressure can cross the threshold for acertain duration (e.g., the at least one parameter crosses the thresholdone time per day for 3 consecutive days, the at least one parametercrosses the threshold one time per day for 5 consecutive days, etc.)before the alert module is configured to generate an alert.

In another example, if, at 1515, the at least one parameter indicativeof an atrial filling pressure has not crossed the threshold, then analert is not generated, and the process flow returns to 1505.

In other examples, the alert can be generated using a threshold or othermethods, including a statistical analysis, a standard deviation, or aconstant false alarm-rate technique, such as is described in theco-pending, commonly assigned Siejko et al. U.S. patent application Ser.No. 11/276,735, entitled “PHYSIOLOGICAL EVENT DETECTION SYSTEMS ANDMETHODS,” filed Mar. 13, 2006, which is hereby incorporated by referencein its entirety.

In the examples of FIGS. 8-15, various examples, including sensing aheart sound signal, sensing a posture signal, sensing a cardiac signal,detecting at least one parameter indicative of an atrial fillingpressure, determining if the at least one parameter indicative of anatrial filling pressure has crossed a threshold, generating an alert,operating or ceasing to operate a system, activating or deactivating amethod, etc., are disclosed. It is to be understood that these examplesare not exclusive, and can be implemented either alone or incombination, or in various permutations or combinations.

It is to be understood that the above description is intended to beillustrative, and not restrictive. For example, the above-describedembodiments (and/or aspects thereof) may be used in combination witheach other. Many other embodiments will be apparent to those of skill inthe art upon reviewing the above description. The scope of the inventionshould, therefore, be determined with reference to the appended claims,along with the full scope of equivalents to which such claims areentitled. In the appended claims, the terms “including” and “in which”are used as the plain-English equivalents of the respective terms“comprising” and “wherein.” Also, in the following claims, the terms“including” and “comprising” are open-ended, that is, a system, device,article, or process that includes elements in addition to those listedafter such a term in a claim are still deemed to fall within the scopeof that claim. Moreover, in the following claims, the terms “first,”“second,” and “third,” etc. are used merely as labels, and are notintended to impose numerical requirements on their objects.

The Abstract is provided to comply with 37 C.F.R. § 1.72(b), whichrequires that it allow the reader to quickly ascertain the nature of thetechnical disclosure. It is submitted with the understanding that itwill not be used to interpret or limit the scope or meaning of theclaims. Also, in the above Detailed Description, various features may begrouped together to streamline the disclosure. This should not beinterpreted as intending that an unclaimed disclosed feature isessential to any claim. Rather, inventive subject matter may lie in lessthan all features of a particular disclosed embodiment. Thus, thefollowing claims are hereby incorporated into the Detailed Description,with each claim standing on its own as a separate embodiment.

1. A system comprising: an implantable medical device, including: aheart sound sensor, configured to sense a heart sound signal of a heart;a heart sound detector, coupled to the heart sound sensor, the heartsound detector configured to detect at least one parameter indicative ofan atrial filling pressure of the heart using the heart sound signal;and a processor, coupled to the heart sound detector, the processorconfigured to compare the at least one parameter to a threshold.
 2. Thesystem of claim 1, wherein the atrial filling pressure includes a leftatrial filling pressure.
 3. The system of claim 1, wherein the at leastone parameter includes at least one measurement, feature,characteristic, computation, or interval of the heart sound signal. 4.The system of claim 3, wherein the at least one measurement, feature,characteristic, computation, or interval of the heart sound signalincludes at least one of an amplitude of a third heart sound (S3), asplit second heart sound (S2) time interval, an S2-S3 time interval, anda normalized amplitude or interval of at least one measurement, feature,or characteristic of the heart sound signal.
 5. The system of claim 1,wherein the implantable medical device includes a cardiac sensor,coupled to the heart sound detector, the cardiac sensor configured tosense a cardiac signal of the heart; and wherein the heart sounddetector is configured to detect the at least one parameter using theheart sound signal and the cardiac signal.
 6. The system of claim 5,wherein the at least one parameter includes at least one measurement,feature, characteristic, computation, or interval between at least onecardiac signal feature and at least one heart sound signal feature. 7.The system of claim 5, wherein the at least one parameter includes asystolic time interval (STI).
 8. The system of claim 1, wherein thethreshold includes a predefined threshold.
 9. The system of claim 1,wherein the threshold includes an absolute threshold.
 10. The system ofclaim 1, including a posture sensor, coupled to the processor, theposture sensor configured to sense a posture signal; and wherein theprocessor is configured to compare the at least one parameter to thethreshold using the posture signal.
 11. The system of claim 1, includingan alert module, coupled to the processor, the alert module configuredto generate an alert using the at least one parameter.
 12. The system ofclaim 11, wherein the alert is configured to be generated with apredefined specificity.
 13. The system of claim 12, wherein the alert isconfigured to be generated with a predefined specificity equal to orgreater than 85%.
 14. The system of claim 13, wherein the alert isconfigured to be generated with a predefined specificity equal to orgreater than 90%.
 15. A system comprising: means for sensing a heartsound signal of a heart using an implanted heart sound sensor; means fordetecting at least one parameter indicative of an atrial fillingpressure of the heart using the heart sound signal; and means forcomparing the at least one parameter to a threshold.
 16. A methodcomprising: sensing a heart sound signal of a heart using an implantedheart sound sensor; detecting at least one parameter indicative of anatrial filling pressure of the heart using the heart sound signal; andcomparing the at least one parameter to a threshold.
 17. The method ofclaim 16, wherein detecting the at least one parameter indicative of anatrial filling pressure includes detecting at least one parameterindicative of a left atrial filling pressure.
 18. The method of claim16, wherein detecting the at least one parameter includes detecting atleast one measurement, feature, characteristic, computation, or intervalof the heart sound signal.
 19. The method of claim 18, wherein detectingthe at least one measurement, feature, characteristic, computation, orinterval of the heart sound signal includes detecting at least one of anamplitude of a third heart sound (S3), a split second heart sound (S2)time interval, an S2-S3 time interval, and a normalized amplitude orinterval of at least one measurement, feature, or characteristic of theheart sound signal.
 20. The method of claim 16, including: sensing acardiac signal of the heart using an implanted cardiac sensor; andwherein detecting the at least one parameter includes using the heartsound signal and the cardiac signal.
 21. The method of claim 20, whereindetecting the at least one parameter includes detecting at least onemeasurement, feature, characteristic, computation, or interval betweenat least one cardiac signal feature and at least one heart sound signalfeature.
 22. The method of claim 20, wherein detecting the at least oneparameter includes detecting at least one systolic time interval (STI).23. The method of claim 16, wherein comparing the at least one parameterto a threshold includes comparing the at least one parameter to apredefined threshold.
 24. The method of claim 16, wherein comparing theat least one parameter to a threshold includes comparing the at leastone parameter to an absolute threshold.
 25. The method of claim 16,including: sensing a posture signal using a posture sensor; and whereincomparing the at least one parameter to a threshold includes using theposture signal.
 26. The method of claim 16, including generating analert using the at least one parameter.
 27. The method of claim 26,wherein generating an alert includes generating an alert with apredefined specificity.
 28. The method of claim 27, wherein generatingan alert with a predefined specificity includes generating an alert witha predefined specificity of at least 85%.
 29. The method of claim 28,generating an alert with a predefined specificity includes generating analert with a predefined specificity of at least 90%.